PROVENANCE OF EARLY PALEOGENE STRATA IN THE HUERFANO BASIN: IMPLICATIONS FOR UPLIFT OF THE WET MOUNTAINS, COLORADO, USA

Sedimentary basins within the Western Interior of North America preserve a record of Late Cretaceous through latest Eocene sedimentation derived from flanking Laramide uplifts. In northern and western basins, the strata contain a well-documented proxy history of Laramide-style exhumation and regional climatic conditions. More southerly basins, such as the Huerfano Basin located in south-central Colorado, are comparatively understudied despite being key in understanding the spatiotemporal progression of Laramide tectonism and regional climatic gradients.

In this study we present a comprehensive analysis of provenance for the Poison Canyon, Cuchara, and Huerfano formations in the Huerfano Basin. As part of our provenance analysis, we characterized gravel clast composition, petrographic compositions of fluvial sandstones (n = 31 thin sections), and U–Pb detrital zircon age spectra (n = 848 age determinations) from sand-bodies within each of the three formations. The results indicate a new unroofing and source history for the sediment within the basin that contradicts previous hypotheses.

Arkose sand-bodies lacking lithic fragments and arc-derived, Mesozoic-aged zircon populations from the Western Cordilleran are inconsistent with recycling of the sedimentary carapace as previously suggested. Diagnostic zircon peaks at 516-517 Ma, 1423-1430 Ma, and 1678-1687 Ma show that sediment delivered to the Huerfano Basin did not derive from the San Luis Highlands or incipient Sangre de Cristo Mountains to the west, but that the Precambrian crystalline core and associated Cambrian plutons of the Wet Mountains to the northeast were exposed by the time Laramide deposition initiated in the basin. There are no major provenance shifts upsection, indicating a largely stable or lithologically uniform sediment source from the Paleocene through at least ~51 Ma. This suggests the major changes in deposition are more likely related to tectonic and climatic conditions rather than lithologic controls on stratigraphic patterns.